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Low carbon steel with carbon content ranging from 0.15% to 0.3% cannot be hardened through quenching and tempering processes and there is little to no martensitic transformation occurring upon quenching. To improve the surface hardness, carburizing is commonly employed. Through this treatment, the surface composition of the low-carbon steel is altered by the diffusion of carbon, resulting in a hard outer casing with good wear resistance. This work investigates the effect of the carburizing treatment temperature and holding time on the crystallographic structure, hardness, and hardened surface layer dimension of commercial low-carbon steel 16NC6. The steel was carburized at 900°C for different holding times of 1, 2, and 3 hours. After the carburizing and quenching processes, the hardness values and the morphology of the crystallographic structure were measured and characterized.

Hard coatings based on chromium carbides and chromium borides are widely used in applications that require mechanical performance, i.e., high hardness and low friction coefficient and good corrosion resistance. In this work, we made layers of chromium carbides and chromium borides on the surface of low carbon steel through some specific treatments. For chromium carbides, the cementation in a solid medium followed by electroplating of chromium on the surface and finally the application of annealing treatment at temperatures between 500 and 1100 °C for 1 hour. For chromium borides, the boriding treatment in solid medium at 900 °C for 4 hours followed by chromium electroplating on the steel surface and finally the application of annealing treatment at temperatures at 950 °C for 1 and 2 hours. The obtained results show that, in the first case, the cemented layer and the chromium deposited on the surface combine to form chromium carbides on the treated surface after annealing. Similarly, for the second case, boron diffusion and chromium deposition lead to chromium borides on the treated surface. The characteristics of the chromium carbides and chromium borides obtained are very similar to those of chromium carbides and chromium borides obtained by other processes.

Steel substrates low carbons were face-hardened by cementing in case, and then thin layers of chromium were deposited by electrolytic way on these substrates. After deposition, the samples were exposed to isothermal annealing in the temperature of 950°C. The characterization of the thin layers was made by means of optical microscopy and interferometry Vickers micro-hardness. From the obtained results, we have established the kinetics of phase shift (under effect the layer of cementing) in the thin layers of chromium which are transformed into chromium carbide while passing by metastable phases of transition. These transformations occurred by diffusion of the carbon atoms coming from layer of cementing, germination and growth in solid phase. This fact has examined according to the temperature of annealing, the evolution of the lattice parameter and the morphology of the deposited chromium layer. As regards the mechanical properties, it was established that the micro-hardness believes with the evolution of the phase shift.

Low carbon steel substrates were face-hardened by cementing, after which thin layers of chromium were deposited electrolytically on these substrates. After deposition, the samples were exposed to isothermal annealing at a temperature of 950°C. The characterization of the thin layers was carried out by means of optical microscopy and interferometry using the Vickers microhardness test. The obtained results allowed establishing the phase shift kinetics (under the effect of the cementing layer) in thin layers of chromium, which are transformed into chromium carbide when passing through metastable transition phases. These transformations were due to diffusion of the carbon atoms coming from the layer of cementing, germination and growth in solid phase. This fact has been examined taking into account the annealing temperature, the lattice parameter evolution and the deposited chromium layer morphology. As to mechanical properties, it was established that the micro-hardness depends on the phase shift evolution

The present study has been conducted in order to obtain titanium carbide layer using a conversion treatment consisting of two main steps. In the first step a thin pure titanium layer was deposited onto 120C4 carbon steel by PVD. In a second step, a vacuum annealing treatment is conducted in order to diffuse the carbon atoms from the substrate toward the titanium coating. As a result, the pure titanium coating is transformed into titanium carbide. However, depending on the annealing temperature, partial or complete conversion into TiC is obtained. Due to that the hardness of the layer depends on the annealing temperature. By a systematic study of the hardness-load variation, the process of the phase transformation of the layer is then confirmed.

International audience; For an accurate determination of the materials hardness, instrumented indentation test is undoubtedly the most adequate technique compared to the classical one. However, numerous laboratories or industries have no access to such instrumented device. Consequently, they have no other alternative methods that the use of classical indentation test. However, this technique can lead to wrong interpretation because it does not allow considering the indenter tip defect.In this paper, we suggest to introduce the indenter tip defect into the classical hardness calculation. The proposed methodology is validated on a diamond like-carbon thin film deposited onto a tungsten carbide. Firstly, the truncated indenter tip defect length is estimated from the indentation size effect observed for the substrates which is attributed to the influence of the indenter tip defect. As a result, the tip defect is found to have the same value independently of the tested samples. Afterwards, the tip defect length is introduced into the composite hardness computation and the model of Jönsson and Hogmark is applied to predict film hardness. As a main result, the film hardness is found equal to 37.3 GPa independently of the film thickness and in a good accordance with literature data regarding the diamond hybridization sp3/sp2 ratio.

The surface areas of the parts subjected to mechanical loads influence to a great extent the resistance to wear and fatigue. In majority of cases, producing of a hard superficial layer on a tough substrate is conducive to an increased resistance to mechanical wear and fatigue. Cementation treatment of low alloy steels which bonds superficial martensitic layer of high hardness and lateral compressive to a core of lower hardness and greater toughness is an example of a good solution of the problem. The high hardness of the martensitic layer is due to an increased concentration of interstitial carbon atoms in the austenite before quenching. The lower hardness of the core after quenching is due to the presence of ferrite and pearlite components which appear if the cooling rate after austenitization becomes lower than the critical on. The objective of the present study was to obtain a cemented surface layer on low alloy steel by means of pack carburizing treatment. Different steel grades, austenitization temperatures as well as different soaking times were used as parameters of the pack carburizing treatment. During this treatment, carbon atoms from the pack powder diffuse toward the steels surface and form compounds of iron carbides. The effect of carburizing parameters on the transformation rate of low carbon surface layer of the low alloy steel to the cemented one was investigated by several analytical techniques.